Embodiments of the present invention relate to the measurement of the gas flow properties of gas nozzles of a gas distributor used for distributing gas in a substrate processing apparatus.
In the fabrication of electronic circuits and displays, semiconductor, dielectric and conductor materials are deposited and patterned on a substrate, such as a silicon wafer, compound semiconductor wafer, or dielectric plate. These materials are formed by chemical vapor deposition (CVD), physical vapor deposition (PVD) processes, oxidation, nitridation, ion implantation, and other processes. For example, in CVD, a process gas is introduced into a chamber and energized by heat or RF energy to deposit a film on the substrate. In PVD, a target is sputtered with process gas to deposit a layer of target material onto the substrate. In etching, a patterned mask comprising a photoresist or hard mask, is formed on the substrate surface by lithography, and portions of the substrate surface that are exposed between the mask features are etched by an energized process gas.
In such processes, the substrate processing chambers comprise gas distributors with gas showerheads, plates and other structures, which have a plurality of gas nozzles to introduce the desired process gas in the chamber. For example, the gas distributor can comprise a showerhead having a faceplate with a large number of holes, such as, for example, from 1000 to 9000 holes. In another version, the gas plate is an annular ring with circularly spaced-apart gas nozzles, which is positioned about a sidewall of the chamber to inject gas laterally and from around the periphery of the substrate into the chamber. In another version, the gas plate comprises a circular band having from about 100 to about 500 gas nozzles that inject gas vertically into the chamber from around the perimeter of the substrate. In still a further version, the gas plate is a circular ring about the sputtering target with gas nozzles that direct gas from around the target toward the substrate.
In any of these illustrative embodiments of the gas plates, the gas pressure, flow rate, density, or velocity of a gas stream passing through a gas nozzle affects the processing uniformity of a layer being processed on the substrate. However, conventional gas plates often fail to provide a uniform gas flow distribution across the surface of the substrate being processed in the chamber. For example, the gas nozzles of a particular gas plate can generate gas streams having pressures, flow rates, or velocities that vary from one gas nozzle to another nozzle. It is believed that the gas nozzles machined into the gas plate provide such different gas flow characteristics because of small differences in the diameters or lengths of the gas nozzles. For example, the gas nozzles can have different sized diameters because the machining tool used to machine out the gas nozzles gradually wears out over a period of drilling hundreds or thousands of such holes across a gas plate. Initially, the machining tool produces holes having a fixed diameter, but as the machining tool wears out, the machined holes can have larger diameters created by a blunt tool or smaller diameters created by a worn machining tool having a smaller diameter itself. Furthermore, the gas nozzles can require machining tolerances of less than 2/10 mils, which is so tight that even a slightly worn machining tool does not meet the tolerances. A worn machining tool can also create surface defects in the sidewalls of the gas nozzles, such as burrs, cracks, and the like, as the cutting properties of the tool deteriorate.
Gas flow measuring apparatus have also been developed to measure the gas flow characteristics of individual gas nozzles of a gas plate, or even the average flow characteristics of a quadrant of the gas nozzles. For example, commonly assigned, U.S. patent application Ser. No. 11/754,244 to Sun et al., entitled “GAS FLOW CONTROL BY DIFFERENTIAL PRESSURE MEASUREMENTS”, which is incorporated by reference herein and in its entirety, describes measuring the flow properties of an individual gas nozzle, or a single measurement of the average gas flow properties of an entire quadrant of nozzles, or a single measurement of all the nozzles of the entire gas plate. The described gas flow measuring apparatus uses a differential pressure measuring device which operates using a gas pressure analog of a Wheatstone bridge resistance device. However, such measuring apparatus can be relatively slow in operation when measuring the individual gas flow properties of every single gas nozzle of a gas plate having a large number of nozzles, for example, at least 100 nozzles or even at least 300 nozzles. Such an apparatus also cannot easily measure the individual properties of a large number of gas nozzles in a simultaneous, time-effective manner.
Still further, conventional techniques to measure the surface roughness, smoothness, or other quality of the inside surfaces of gas nozzles are difficult to implement. The surface smoothness or roughness of the nozzle sidewall surfaces can affect the properties of the layer being processed on the substrate. For example, gas nozzles with the rougher sidewalls can cause deposition of a slightly thinner layer on the substrate portion facing the central portion of the gas nozzle, and thicker deposition annulus facing the circumference of the nozzle. Further, when material is being etched using etchant gas emitted from gas nozzles having rough or poorly machined uneven surfaces, the substrate portion facing the center of the gas nozzle is often etched more quickly than the substrate portion facing the circumference of the gas nozzle. This unevenness in gas nozzle surfaces can occur from grain smearing effects, or when a machining tool used to form the holes of the gas nozzles gradually wears out over time, resulting in some gas nozzles having sidewalls with rougher surfaces than the nozzles which were initially machined. However, conventional surface roughness methods made with profilometers (which run a needle probe across a surface to measure its surface roughness) are difficult to implement inside the small diameters of gas nozzles without cutting open the nozzle, and often also do not provide accurate surface roughness measurements.
For various reasons that include these and other deficiencies, and despite the development of various gas nozzle measurement apparatus and methods, further improvements in the measurement of gas flow properties of individual gas nozzles are continuously being sought.